Winches are used in many applications to move payloads via spoolable media, such as metal, synthetic or fibre cables, wires and ropes. Typically, a winch includes a drum or spool around which a spoolable medium is wound, wherein rotation of the drum permits spooling of the medium.
In some species of winch the drum also acts to store the spoolable medium, with the medium be arranged in single or multiple wraps and layers between end flanges of the drum. In such winch species, however, the spoolable medium may be subject to significant radial crushing forces, particularly in circumstances where large payloads are involved and thus significant tensions are applied to the spoolable medium. Further, in some applications it may be necessary to store the medium in a high tension state, which may reduce the life span of the medium through fatigue, excessive strains, hysteresis and the like. Furthermore, storage of the spoolable medium on a drum typically requires the use of complex fleeting arrangements to ensure that the medium is arranged in suitable wraps and layers.
In other species of winch the drum is used only to apply a force to a spoolable medium, with the spoolable medium being stored separately, for example in a basket, on a separate spool or the like. The force applied by the drum is typically either a pulling force to pay in a spoolable medium, or a controlled releasing force to permit controlled paying out of a spoolable medium while under load, for example while connected to a payload. In such winch species, which may include capstan or windlass winches, an intermediate portion of a spoolable medium is wrapped around the drum a number of times such that an outboard side of the spoolable medium extends from the drum to engage a payload, and an inboard side of the spoolable medium extends to storage. Under loaded conditions the drum functions to reduce the tension in the spoolable medium from a high tension condition in the outboard side, to a lower tension condition in the inboard side of the spoolable medium, thus permitting the spoolable medium to be stored in a favourable low tension state. In view of this tension reduction functionality, such winch species are often called detensioning units. In use, the drum establishes a tension gradient in the spoolable medium, which may be defined by the capstan friction equation:
            T      1              T      2        =      ⅇ    μθ      wherein:            T1=outboard tension        T2=inboard tension        μ=co-efficient of friction between the spoolable medium and the drum or contact surface        θ=angle of contact with the drum (e.g., one wrap is 2π radians)        
In existing winch devices the tension gradient may not be evenly distributed across the spoolable medium in contact with the drum, which may result in non-uniform tension reduction with possible adverse effects on the medium, such as variable strain distribution and the like.
In such capstan style winch species, arrangements are typically made to ensure that the spoolable medium follows a defined path around the drum to ensure appropriate separation between adjacent wraps, provide appropriate take off points for both outboard and inboard sides, prevent piling or bunching at flanged ends of the drum, and the like. These arrangements may include the use of grooves or flutings on the surface of the drum, the use of knives or fleeting rings and the like. GB 2 009 077, GB 1 425 016 and WO 00/10903 each discloses arrangements in which drum grooves are utilised.
However, such arrangements for suitably handling a spoolable medium along a desired path may involve complex mechanisms, which may be expensive and subject to failure. Further, existing arrangements may not adequately handle features of a spoolable medium, such as splices, connectors, sockets and the like. Also, existing arrangements, such as knives or fleeting rings, may result in adverse twisting of the spoolable medium, and can increase the frictional forces applied to the medium, which may result in abrasion or other damage which may affect mechanical integrity.